1. Field of the Invention
The present invention relates generally to gas turbine engines and, more particularly, to a fluid-carrying tube coupling assembly with an internal seal and drain arrangement for use on such engines.
2. Description of the Prior Art
Gas turbine engines typically include a core engine covered by a cowl. The core engine has a compressor for compressing air entering the core engine, a combustor where fuel is mixed with the compressed air and then burned to create a high energy gas stream, and a first or high pressure turbine which extracts energy from the gas stream to drive the compressor.
The area of the core engine covered by the cowl is known as a "fire zone". Pipes or tubes carrying flammable fluids within this fire zone must be made to comply with fire prevention regulations. For example, a fuel-carrying tube within the fire zone must be able to withstand 2000.degree. F. for five minutes, whereas an oil-carrying tube must be able to withstand 2000.degree. F. for fifteen minutes. Furthermore, components are designed to ensure against any single failure causing ignition of a fire so that in most instances a dual failure is necessary before a fire ignition will occur.
Fire prevention in the fire zone is dependent upon providing a component design which will not allow leakage of flammable fluids to come in contact with an ignition source, such as a spark or surface which is above the auto-ignition temperature for that fluid. One potential source of leakage of flammable fluid is from a fitting or coupling between fluid-carrying tubes in the fire zone. Fluid leakage is typically due to maintenance errors, damage to seal surfaces, overpressure and/or loosening caused by an unfavorable environment. Improved coupling designs to reduce, if not eliminate entirely, the potential for flammable fluid leakage to cause a fire are sought after on a continuing basis.
SUMMARY OF THE INVENTION
The present invention provides a fluid-carrying tube coupling assembly designed to satisfy the aforementioned needs. The tube coupling assembly of the present invention incorporates a seal and drain arrangement which is designed, first, to prevent fluid leakage from occurring at all and, second, in the event leakage does occur, to constrain the leaking fluid to exit the coupling assembly in a direction selected to minimize the risk of leaking fluid contacting autoignition temperatures. The selected direction of the leaking fluid flow can be oriented away from an ignition source. While the fluid-carrying tube coupling assembly of the present invention is applicable to any equipment having tubes carrying flammable or hazardous fluids, it is particularly suited to flight vehicles where fire prevention is a prime consideration.
Accordingly, the present invention is directed to a fluid-carrying tube coupling assembly for use in a gas turbine engine. The tube coupling assembly comprises a pair of fitting members each including an inner hub portion and an outer flange portion, a seal and drain arrangement between the outer flange portions of the fitting members, and means for releasably clamping the fitting members to one another at the outer flange portions thereof.
The inner hub portions of the fitting members are attachable to ends of at least a pair of respective fluid-carrying hollow tubes. Also, the inner hub portions are disposed relative to one another so as to define at least one flow passage providing fluid communication between the hollow tubes.
The outer flange portions of the fitting members are attached to and extend radially outwardly from the respective inner hub portions. Also, the outer flange portions are disposed relative to one another so as to define an annular interface region between the fitting members which provides a path of potential fluid leakage from the flow passage to the exterior of the fitting members.
The seal and drain arrangement is defined at the interface region between the outer flange portions of the fitting members. The seal and drain arrangement includes an inner annular primary seal within the annular interface between the fitting members. The primary seal encircles the flow passage of the inner hub portions so as to obstruct the path of potential fluid leakage from the flow passage to the exterior of the fitting members.
Also, the seal and drain arrangement includes a drain channel within the annular interface region between the fitting members. The drain channel encircles the inner annular primary seal so as to intersect the path of potential fluid leakage from the flow passage to the exterior of the fitting members in the event of failure of the primary seal.
Further, the seal and drain arrangement includes an outer annular secondary seal within the annular interface region between the fitting members. The outer annular secondary seal encircles the drain channel so as to obstruct the path of potential fluid leakage from the flow passage to the exterior of the fitting members in the event of failure of both the primary seal and the drain channel.
These and other features and advantages and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.